Production method of suspension board with circuit

ABSTRACT

A method of producing a suspension board with circuit, wherein after an insulating base layer is formed on a metal supporting board, a conductive pattern including a ground wiring pattern and a signal wiring pattern is formed on the insulating base layer. Then, an insulating cover layer to cover the conductive pattern is formed on the insulating base layer in such a manner that a first cover opening portion and a second cover opening portion are formed in the insulating cover layer. Then, an electrolytic plating layer is formed on a surface of the ground terminal exposed from the first cover opening portion and on a surface of the ground connecting portion exposed from the second cover opening portion, feeding electric power from the ground wire. Thereafter, a metal filling layer is formed in the base opening portion to electrically connect the ground connecting portion and the metal supporting board.

CROSS REFERENCE TO RELATED APPLICATION

This application corresponds to Japanese Patent Application No. 2005-241687 filed with Japanese Patent Office on Aug. 23, 2005, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a production method of a suspension board with circuit and, more particularly, to a production method of a suspension board with circuit having a ground terminal.

2. Description of the Prior Art

In recent years, improvements in transmission speed and transmission accuracy are increasingly demanded for storage units, such as computers and their peripheral devices. In the circumstances, there are increasing tendencies to use high-frequency signals for electric signals. However, noises in electric signals transmitted increase with higher frequency.

In general, a suspension board with circuit mounted on a hard disc comprises an insulating layer formed on a base material of a metal foil serving as a metal supporting board, and a conductor layer serving as a conductive pattern formed on the insulating layer (Cf. JP Laid-open (Unexamined) Patent Publication No. Hei 10-265572, for example). In this suspension board with circuit, a difference in the electrical potentials between the metal supporting board and the conductive pattern may cause a noise.

In order to reduce such a noise, the suspension board with circuit is structured so that a ground terminal is formed in the conductive pattern for connecting the metal supporting board, so as to conduct the conductive pattern and the metal supporting board for ground connection by connecting the ground terminal of the conductive pattern with a ground terminal of an electronic component such as a magnetic head.

Further, in order to prevent corrosion, a gold plating layer is formed on the ground terminal by electrolytic gold plating.

The gold plating layer is formed on the ground terminal in the following manner. First, the suspension board with circuit 1 before trimming is covered with a plating resist 21 so that only a ground terminal 18 forming portion of the conductive pattern 4 is exposed from the plating resist 21, as shown in FIG. 6( a). Then, a gold plating layer 6 is formed on the ground terminal 18 forming portion of the conductive pattern 4 by electrolytic gold plating, while feeding electric power from the metal supporting board 2, as shown in FIG. 6( b). Thereafter, the plating resist 21 is removed, as shown in FIG. 6( c). In FIG. 6, the same reference numerals and marks are labeled to corresponding parts to those shown in FIG. 1.

In the method illustrated above, since the electric power is fed from the metal supporting board 2, the whole area of the suspension board with circuit 1 except the ground terminal 18 forming portion of the conductive pattern 4 must be covered with the plating resist 21 in order to prevent the gold plating layer 6 from being formed on the metal supporting board 2. On the other hand, the formation of the plating resist 21 and the subsequent removal process of the same require cumbersome and complicated processes, such as adhesion, exposure-to-light, development, and stripping of the plating resist 21, thus increasing production cost.

SUMMARY OF THE INVENTION

It is the object of the invention to provide a production method of a suspension board with circuit that can form a ground terminal for connection with the ground, and reduce production cost, while reducing the number of man-hours and complicated process.

The present invention provides a production method of a suspension board with circuit comprising the step of preparing a metal supporting board, the step of forming on the metal supporting board an insulating base layer having a base opening portion from which the metal supporting board is exposed, the step of forming on the insulating base layer a conductive pattern comprising ground wires, the step of forming on the insulating base layer an insulating cover layer covering the conductive pattern and having a first cover opening portion from which a part of the ground wire is exposed, and a second cover opening portion from which the base opening portion is exposed together with a part of the ground wire, the step of forming an electrolytic plating layer on a surface of the ground wire exposed from the first cover opening portion and on a surface of the ground wire exposed from the second cover opening portion, feeding electric power from the ground wire, and the step of forming a metal filling layer in the base opening portion so as to electrically connect the ground wire and the metal supporting board.

In the production method of the suspension board with circuit of the present invention, after the first cover opening portion from which a part of the ground wire is exposed and the second cover opening portion from which a part of the ground wire is exposed together with the base opening portion are formed, the electrolytic plating layer is formed, by feeding electric power from the ground wire. Thereafter, the metal filling layer is formed in the base opening portion, so as to electrically connect the ground wire and the metal supporting board. This provides the result that the electrolytic plating layer can be formed on part of the ground wire without any need for covering the metal supporting board with the plating resist, and can electrically connect the ground wire and the metal supporting board for connection with the ground thereafter. As a result of this, the ground terminal can be formed, while reducing the number of man-hours and complicated processes for forming the electrolytic plating layer, thus achieving the production cost reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a plan view of a principal part of an embodiment of a suspension board with circuit produced by a production method of a suspension board with circuit of the present invention,

FIG. 2 is an enlarged sectional view of the same taken along line A-A of FIG. 1,

FIG. 3 is and enlarged sectional view of the same taken along line B-B of FIG. 1,

FIG. 4 is a process drawing showing an embodiment of a production method of a suspension board with circuit of the present invention:

(a) showing the process of preparing a metal supporting board;

(b) showing the process of forming an insulating base layer on the metal supporting board in a pattern having a base opening portion;

(c) showing the process of forming a thin metal film on the entire surface of the insulating base layer and on the entire surface of the metal supporting board exposed from the base insulating layer;

(d) showing the process of forming on the thin metal film a plating resist of a pattern reverse to a conductive pattern;

(e) showing the process of forming the conductive pattern on the thin metal film exposed from the plating resist;

(f) showing the process of removing the plating resist; and

(g) showing the process of removing the thin metal film exposed from the conductive pattern,

FIG. 5 is a process drawing, which is the subsequence of FIG. 4, showing the embodiment of the production method of the suspension board with circuit:

(h) showing the process of forming an insulating cover layer to cover the conductive pattern in a pattern to form a first cover opening portion and a second cover opening portion on the insulating cover layer;

(i) showing the process of forming a base opening portion in the metal supporting board to correspond in position to a part of the conductive pattern;

(j) showing the process of forming an electrolytic plating layer on a surface of a ground wiring including a ground terminal exposed from the first cover opening portion and on a surface of a ground connecting portion exposed from the second cover opening portion by feeding electric power from the ground wiring; and

(k) showing the process of forming a metal filling layer in the base opening portion to electrically connect the ground wiring and the metal supporting board, and

FIG. 6 is a process drawing showing an embodiment of a production method of a conventional suspension board with circuit:

(a) showing the process of covering the suspension board with circuit before trimming, with a plating resist so that only a ground terminal forming portion of a conductive pattern is exposed from the plating resist;

(b) showing the process of forming a plating layer on the ground terminal forming portion of the conductive pattern by electrolytic plating, while feeding electric power from the metal board; and

(c) showing the process of removing the plating resist.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a plan view of a principal part (from which an electrolytic plating layer is omitted) of an embodiment of a suspension board with circuit produced by a production method of a suspension board with circuit of the present invention. FIG. 2 is an enlarged sectional view of the same taken along line A-A of FIG. 1, and FIG. 3 is an enlarged sectional view of the same taken along line B-B of FIG. 1.

The suspension board with circuit 1 comprises, as shown in FIG. 2, a metal supporting board 2, an insulating base layer 3 formed on the metal supporting board 2, a conductive pattern 4 formed on the insulating base layer 3 to be in the form of a wired circuit pattern, and an insulating cover layer 5 formed on the insulating base layer 3 to cover the conductive pattern 4.

This suspension board with circuit 1 further comprises, as shown in FIG. 3, an electrolytic plating layer 6 formed on the conductive pattern 4 exposed from a first cover opening portion 16 and from a second cover opening portion 17 mentioned later, and a metal filling layer 7 for electrically connecting a ground wire 14, mentioned later, of the conductive pattern 4 to the metal supporting board 2.

The metal supporting board 2 is in the form of a rectangular sheet, when viewed from top, extending in a longitudinal direction thereof and formed of a metal foil, a thin metal sheet, and the like, as shown in FIG. 1. The metal supporting board 2 has a base opening portion 12 formed to correspond in position to a part of the conductive pattern 4, as shown in FIG. 3.

The insulating base layer 3 is formed on the metal supporting board 2 in the form of a rectangular sheet slightly smaller in longitudinal dimension than the metal supporting board 2, when viewed from top, as shown in FIGS. 1 and 3. The base opening portion 13 from which the metal supporting board 2 is exposed is formed in the insulating base layer 3.

The base opening portion 13 is formed in one lengthwise end portion of the insulating base layer 3 (hereinafter it is referred to as “the rear end portion”) at a portion thereof where a ground connecting portion 19 mentioned later is formed, as shown in FIG. 3, and is shaped in a circular form (a cylindrical form) when viewed from top.

The conductive pattern 4 is formed in the form of a wired circuit pattern on the insulating base layer 3 and comprises a plurality of wires (three wires) spaced apart from and arranged in parallel with each other along a widthwise direction of the metal supporting board 2 (along a direction orthogonal to the longitudinal direction), as shown in FIG. 1.

The plurality of wires arranged on the insulating base layer 3 extend along the longitudinal direction, comprising the ground terminal 14 for connecting a magnetic head (not shown) with the ground, and a plurality of signal wires (two signal wires) 15 for transmitting input/output electrical signals from/to the magnetic head (not shown).

The ground wire 14 has a ground terminal 18 formed at the other lengthwise end portion thereof (hereinafter it is referred to as “the front end portion”), and a ground connecting portion 19 formed at the rear end portion. The ground terminal 18 is formed in the form of a square land larger in width than the ground wire 14. The ground connecting portion 19 is larger in diameter than the base opening portion 13 and is shaped like a ring surrounding the base opening portion 13.

Each of the signal wires 15 has a head terminal 15 a formed at the front end portion for connecting with the magnetic head (not shown), and an external terminal 15 b formed at the rear end portion for connecting with an external circuit. The head terminal 15 a and the external terminal 15 b are each formed in the form of a square land larger in width than the signal wire 15.

When the conductive pattern 4 is formed by the additive process mentioned later, the thin metal film 11 is interposed between the insulating base layer 3 and the conductive pattern 4, as shown in FIGS. 2 and 3.

The insulating cover layer 5 is formed on the insulating base layer 3 to cover the conductive layer 4. The insulating cover layer 5 is formed in the form of a rectangular sheet, when viewed from top, slightly smaller in the lengthwise dimension than the insulating base layer 3. The first cover opening portions 16 and the second cover opening portion 17 are formed in the insulating cover layer 5.

The first cover opening portions 16 in the front end portion of the insulating cover layer 5 are formed to correspond to the ground terminal 18 and the head terminals 15 a, respectively. The first cover opening portions 16 are each shaped in a generally rectangular form, when viewed from top, and are formed so that the ground terminal 18 and the head terminals 15 a are exposed from their respective first cover opening portions 16.

The second cover opening portion 17 is formed to expose the ground connecting portion 19 and the external terminals 15 b therefrom by placing the rear end of the insulating cover layer 5 forward of the ground connecting portion 19 and the external terminals 15 b so that the insulating cover layer 5 is not formed at the rear end portion of the insulating base layer 3. The ground connection portion 19 and the base opening portion 13 surrounded by the ground connecting portion 19 are both exposed from the second cover opening portion 17.

The electrolytic plating layer 6 is formed on a surface of the ground terminal 18 and surfaces of the respective head terminals 15 a exposed from the first cover opening 16, and on a surface of the ground connecting portion 19 and surfaces of the respective external terminals 15 b exposed from the second cover opening portion 17, as shown in FIG. 3.

The metal filling layer 7 is filled in the base opening portion 13 and in the ground connecting portion 19 continuously so that it contacts with the electrolytic plating layer 6 and the metal supporting board 2 to electrically connect the electrolytic plating layer 6 and the metal supporting board 2.

Now, referring to FIGS. 4 and 5, which are process drawings showing an embodiment of a production method of a suspension board with circuit of the present invention, the production method of the suspension board with circuit 1 is described.

In this method, the metal supporting board 2 is prepared, first, as shown in FIG. 4( a). The metals that may be used for forming the metal supporting board 2 include, for example, stainless steel, 42-alloy, aluminum, copper-beryllium, and phosphor bronze. Stainless steel is preferably used. Preferably, the metal supporting board 2 has a thickness of 10-60 μm, or preferably 15-30 μm.

Then, the insulating base layer 3 is formed on the metal supporting board 2 so that a pattern in which the base opening portion 13 is formed, as shown in FIG. 4( b).

The insulating materials that may be used for forming the insulating base layer 3 include, for example, synthetic resins, such as polyimide resin, polyamide imide resin, acrylic resin, polyether nitrile resin, polyether sulfonic resin, polyethylene terephthalate resin, polyethylene naphthalate resin and polyvinyl chloride resin. Of these synthetic resins, a photosensitive synthetic resin is preferably used for the insulating base layer 3. A photosensitive polyimide resin is further preferably used therefor.

For example, when a photosensitive polyimide resin is used to form the insulating base layer 3 on the metal supporting board 2 in the predetermined pattern, a varnish of a precursor of the photosensitive polyimide resin (a liquid solution of a photosensitive polyamic acid resin) is uniformly coated over the entire surface of the metal supporting board 2, first. Thereafter, the coated photosensitive polyimide resin is dried, to form a coating. Then, the coating is exposed to light through a photo mask. Subsequently, the coating is developed by a known method, such as a dipping method and a spraying method, using a known developing solution such as alkaline developer. Then, the coating is cured by heating at 250° C. or more, whereby the insulating base layer 3 of polyimide resin is formed on the metal supporting board 2 in the pattern in which the base opening portion 13 is formed.

As an alternative to this, the insulating base layer 3 may be formed by adhesively bonding a dry film including the previously formed base opening portion 13 onto the metal supporting board 2 via an adhesive layer, if necessary.

Preferably, the insulating base layer 3 thus formed has a thickness of e.g. 2-30 μm, or preferably 5-20 μm.

Although the base opening portion 13 is shaped in a circular form when viewed from top, in the FIG. 1, it may be shaped in any proper form, such as a rectangular form. When shaped in a circular form when viewed from top, the base opening portion 13 preferably has a diameter of e.g. 30-1,000 μm, or preferably 50-750 μm.

Then, the conductive pattern 4 is formed on the insulating base layer 3 in the predetermined wired circuit pattern mentioned above. The conductive pattern is formed by a known patterning process, such as an additive process and a subtractive process. Preferably, the additive process is used.

When the conductive pattern 4 is formed by the additive method, a thin metal film 11 serving as a seed film is formed on the entire surface of the insulating base layer 3 and on the entire surface of the metal supporting board 2 exposed from the insulating base layer 2, first, as shown in FIG. 4( c).

The thin metal film 11 is formed using a vacuum deposition process, or preferably using a sputter vapor deposition process. Chromium and copper are preferably used as the metal used for forming the thin metal film 11. To be more specific, for example a thin chrome film and a thin copper film are preferably formed in sequence on the entire surface of the insulating base layer 3 and on the entire surface of the metal supporting board 2 exposed from the insulating base layer 3 by the sputter vapor deposition process. Preferably, the thin chrome film has a thickness of 10-600 nm and the thin copper film has a thickness of 50-200 nm.

Then, a plating resist 21 having a reverse pattern to the conductive pattern 4 is formed on the thin metal film 11, as shown in FIG. 4( d). The plating resist 21 is formed in a resist pattern by a known process using e.g. a dry film photoresist which is to be exposed to light and then developed. Then, the conductive pattern 4 comprising the ground wire 14 and the signal wires 15 is formed in the wiring pattern mentioned above on the thin metal film 11 exposed from the plating resist 21 by electrolytic plating, or preferably by electrolytic copper plating, as shown in FIG. 4( e).

The conductive pattern 4 has a thickness of e.g. 2-15 μm or preferably 5-10 μm. Although the ground connecting portion 19 of the ground wire 14 of the conductive pattern 4 is shaped in a ring form in FIG. 1, the ground connecting portion 19 may be shaped in any proper form such as a rectangular form. When the ground wire 14 is shaped in a ring form, it has an inner diameter of e.g. 10-1,000 μm or preferably 20-900 μm.

Then, the plating resist 21 is removed by a known etching process, such as a chemical etching (wet etching), or by stripping, as shown in FIG. 4( f).

Then, the thin metal film 11 exposed from the conductive pattern 4 (or the thin metal film 11 on which the plating resist 21 was formed) is also removed by the known etching process, such as the chemical etching (wet etching), as shown in FIG. 4( g).

Then, the insulating cover layer 5 for covering the conductive pattern 4 is formed on the insulating base layer 3 to form a pattern in which the first cover openings 16 and the second cover opening 17 are formed, as shown in FIG. 5( h).

The same insulating materials as those used for forming the insulating base layer 3 may be used for forming the insulating cover layer 5. Preferably, photosensitive polyimide resin is used for forming the insulating cover layer 5.

For example, when a photosensitive polyimide resin is used to form the insulating cover layer 5 on the insulating base layer 3, a varnish of a precursor of the photosensitive polyimide resin (a liquid solution of a photosensitive polyamic acid resin) is uniformly coated over a surface of the conductive pattern 4, a surface of the insulating base layer 3 exposed from the conductive pattern 4, and surface of the metal supporting board 2 exposed from the insulating base layer 3 first. Thereafter, the coated photosensitive polyimide resin is dried to form a coating. Then, the coating is exposed to light through a photo mask. Subsequently, the coating is developed by a known method, such as a dipping method and a spraying method, using a known developing solution such as alkaline developer. Then, the coating is cured by heating at 250° C. or more, whereby the insulating cover layer 5 of polyimide resin to cover the conductive pattern 4 is formed on the insulating base layer 3 in the pattern in which the first cover opening portions 16 and the second cover opening 17 are formed.

As an alternative to this, the insulating cover layer 5 may be formed by adhesively bonding a dry film including the previously formed first cover opening portions 16 and second cover opening portion 17 onto the insulating base layer 3 including the conductive pattern 4 via an adhesive layer, if necessary.

Preferably, the insulating cover layer 5 thus formed has a thickness of e.g. 1-30 μm, or preferably 2-5 μm.

Although the first cover opening portions 16 in FIG. 1 are shaped in a rectangular form, when viewed from top, to expose independently the ground terminal 18 and the head terminals 15 a therefrom, respectively, the first cover opening portions 16 may be shaped in any proper form, such as a circular form, without any particular limitation on the form. Further, the first cover opening portions 16 may be formed in a single opening large enough to expose collectively all of the ground terminal 18 and the head terminals 15 a therefrom.

The second cover opening portion 17 is in the form of an opening portion in which no insulating cover layer 5 is formed at the rear end portion of the insulating base layer 3, to expose the ground connecting portion 19 and the respective external terminals 15 b therefrom. Modification may be made to the second cover opening portion 17 by, for example, extending the insulating cover layer 5 to the rear end portion of the insulating base layer 3 and also forming a plurality of second cover opening portions 17 to expose independently the ground connecting portion 19 and the external terminals 15 b therefrom, respectively. Further modification may be made thereto so that it can be in the form of a single opening by extending the insulating cover layer 5 to the rear end portion of the insulating base layer 3 to expose collectively all of the ground connecting portion 19 and the external terminals 15 b therefrom.

Then, the base opening portion 12 is formed in the metal supporting board 2 to correspond to a part of the conductive pattern 4, as shown in FIG. 5( i).

The base opening portion 12 is formed in the metal supporting board 2 in the following manner, for example; After an etching resist is formed on the entire area of the metal supporting board 2 except an area for forming the base opening portion 12, the metal supporting board 2 exposed from the etching resist is chemically etched (wet etching) by the dipping method or the spraying method, using an etching solution, such as for example, aqueous ferric chloride. Thereafter, the etching resist is removed.

Then, the electrolytic plating layer 6 is formed on the surface of the ground wire 14 including the ground terminal 18 exposed from the first cover opening portion 16 and on the surface of the ground wire 14 including the ground connecting portion 19 exposed from the second cover opening portion 17, as shown in FIG. 5( j), by feeding electric power from the ground wires 14 exposed from the second cover opening portion 17. The metals that may be used for the electrolytic plating include, for example, copper, nickel, chromium, and gold. Preferably, nickel and gold are used for the electrolytic plating.

To be more specific, an electrolytic nickel plating layer is first formed by the electrolytic nickel plating, feeding the electric power from the ground wires 14. Then, an electrolytic gold plating layer is sequentially formed on the electrolytic nickel plating layer by the electrolytic gold plating, feeding the electric power from the ground wires 14. The electrolytic nickel plating layer has a thickness of e.g. 6 μm or less, or preferably 0.5-4 μm. The electrolytic gold plating layer has a thickness of e.g. 6 μm or less, or preferably 0.5-4 μm.

In this electrolytic plating process, since the ground wires 14 are not in contact with the metal supporting board 2, the electrolytic plating layer 6 is not formed on the metal supporting board 2 even when the electric power is fed from the ground wires 14. Hence, the need for covering the metal supporting board 2 with the plating resist 21 (Cf. FIG. 6) can be eliminated.

Then, a metal filling layer 7 is formed in the base opening portion 13, so as to electrically connect the ground wires 14 and the metal supporting board 2, as shown in FIG. 5( k).

The metal filling layer 7 is formed in the following manner, for example. Solder paste is filled in from the base opening portion 13 to the ground connecting portion 19 until the solder paste protrudes from an upper surface of the ground connecting portion 19 by screen printing, and then the solder paste is melted by heating, thereby to form the metal filling layer 7. The metal filling layer 7 thus formed contacts with the metal supporting board 2 at a lower portion thereof and contacts with the ground connecting portion 19 via the electrolytic plating layer 6 at an upper portion thereof. The metal filling layer 7 has a height (from its deepest portion to its top portion) of e.g. 50-500 μm, or preferably 200-300 μm.

The metal filling layer 7 formed in the base opening portion 13 electrically connects the ground connecting portion 19 and the metal supporting board 2 via the electrolytic plating layer 6. As a result of this, the ground terminal 18 is electrically connected with the metal supporting board 2 via the ground wire 14 and the metal filling layer 7 and thus with the ground.

According to the production method of this suspension board with circuit 1, the ground wire 14 and the electrolytic plating layer 6 are not electrically connected with the metal supporting board 2 before the metal filling layer 7 is formed, as seen from FIG. 5( j). Hence, when the electrolytic plating layer 6 is formed by plating, feeding electric power to the surface of the ground wire 14 exposed from the second cover opening portion 17, the need for covering the suspension board with circuit 1 with the plating resist 21 can be eliminated. Hence, the number of man-hours and complicated processes can be reduced for forming the ground terminal 18, thus achieving the production cost reduction.

Although the embodiment wherein the first cover opening portions 16 and the second cover opening portion 17 are formed in the front end portion and the rear end portion of the insulating cover layer 5 has been described above, the first cover opening portion 16 and the second cover opening portion 17 may be formed to be continuous to each other to be in the form of a single opening. Further, the metal filling layer 7 may be used as the ground terminal 18 without modification.

EXAMPLE

While in the following, the present invention will be described in further detail with reference to Example, the present invention is not limited thereto.

Example 1

A stainless foil of 20 μm thick was prepared as the metal supporting board, first (Cf FIG. 4( a)). Then, after a liquid solution of polyamic acid resin was coated over the metal supporting board, the coated resin was heated at 100° C. to form a coating of the polyamic acid resin. Then, the coating thus formed was exposed to light (405 nm, 650 mJ/cm²) through a photo mask and the exposed-to-light portion thereof was heated at 180° C. Then, the coating was developed using an alkaline developer, whereby the coating was formed into a pattern in which the base opening portion was formed.

Then, the coating thus patterned was heated at 360° C. to be cured (imidized), whereby the insulating base layer of polyimide resin having thickness of 10 μm was formed in a pattern in which the base opening portion was formed (Cf. FIG. 4( b)). The base opening portion had a circular shape, when viewed from top, having a diameter of 750 μm.

Then, a thin metal film comprising a thin chromium film having a thickness of 30 nm and a thin copper film having a thickness of 60 nm were formed in sequence on the entire surface of the insulating base layer and on the entire surface of the metal supporting board exposed from the insulating base layer by the sputter vapor deposition process (Cf. FIG. 4( c)). Then, a plating resist reverse to the conductive pattern was formed on the thin metal film using a dry film photoresist (Cf. FIG. 4( d)).

Subsequently, the conductive pattern was formed on the thin metal film exposed from the plating resist by electrolytic copper plating (Cf. FIG. 4( e)). Then, after the plating resist was removed by the chemical etching process (Cf. FIG. 4( f)), the thin metal film in an area where the plating resist had been formed were removed by the chemical etching process (Cf. FIG. 4( g)).

The conductive pattern was formed in a wiring pattern of 10 μm thick comprising a signal wiring pattern and a ground wiring pattern. The ground connecting portion of the ground wiring pattern was shaped in a ring form having an inner diameter of 900 μm.

Then, after a liquid solution of polyamic acid resin was coated over the insulating base layer including the conductive pattern, the coated resin was heated at 100° C. to form a coating of the polyamic acid resin. Then, the coating thus formed was exposed to light (405 nm, 1,200 mJ/cm²) through a photo mask and the exposed-to-light portion thereof was heated at 180° C. Then, the coating was developed using an alkaline developer. As a result of this, the coating was developed in a pattern to cover the conductive pattern in which the first cover opening portion and the second cover opening portion were formed.

Then, the coating thus patterned was heated at 360° C. to be cured (imidized), whereby the insulating cover layer of polyimide resin having a thickness of 4 μm was formed to have the pattern in which the first cover opening portion and the second cover opening portion were formed (Cf. FIG. 5( h)).

Thereafter, an etching resist was formed on the entire area of the metal supporting board except an area thereof where the base opening portion was formed. Then, the metal supporting board exposed from the etching resist was chemically etched using an aqueous ferric chloride. Thereafter, the etching resist is removed to form the base opening portion (FIG. 5( i)).

Then, an electrolytic nickel plating layer and an electrolytic copper layer were formed in sequence on a surface of the ground wire including the ground terminal exposed from the first cover opening portion and on a surface of the ground wire including the ground connecting portion exposed from the second cover opening portion, using the ground wire exposed from the second cover opening portion as a lead of the electrolytic plating. The electrolytic plating layer comprising the electrolytic nickel plating layer of 1.0 μm thick and the electrolytic gold plating layer of 2.0 μm thick was formed (CF. FIG. 5( j).

Then, solder paste was filled in the base opening portion by screen printing to electrically conduct the ground connecting portion and the metal supporting board. Thereafter, the solder paste was subjected to a reflow soldering to form a metal filling layer, for the ground connection (CF. FIG. 5( k)). The suspension board with circuit was obtained by the manner described above.

While the illustrative embodiments of the present invention are provided in the above description, such is for illustrative purpose only and it is not to be construed restrictively. Modification and variation of the present invention that will be obvious to those skilled in the art is to be covered by the following claims. 

1. A method of producing a suspension board with circuit, comprising: preparing a metal supporting board; forming on the metal supporting board an insulating base layer having a base opening portion from which the metal supporting board is exposed; forming on the insulating base layer a conductive pattern comprising a ground wire; forming on the insulating base layer an insulating cover layer covering the conductive pattern and having a first cover opening portion in said insulating cover layer from which a part of the ground wire is exposed, and a second cover opening portion in said insulating cover layer from which the base opening portion is exposed together with a part of the ground wire; forming an electrolytic plating layer on a surface of the ground wire exposed from the first cover opening portion and on a surface of the ground wire exposed from the second cover opening portion, by feeding electric power from the ground wire; and after forming the electrolytic plating layer, then forming a metal filling in the base opening portion so as to electrically connect the ground wire and the metal supporting board.
 2. The method according to claim 1, wherein the feeding of electric power from the ground wire is carried out through the part of the ground wire exposed through the second cover opening portion.
 3. The method according to claim 1, wherein the forming of the metal filling comprises filling a solder paste in from the base opening portion to a ground connecting portion of the ground wire until the solder paste protrudes from an upper surface of the ground connecting portion. 